. A contribution to American thalassography : Three cruises of the United States Coast and geodetic survey steamer "Blake", in the gulf of Mexico, in the Caribbean sea, and along the Atlantic coast of the United States, from 1877 to 1880. Blake (Steamer); Marine animals -- Atlantic Ocean; Marine sediments. 116 THREE CRUISES OF THE "; further examination showed these tufts to be bunches of minute spines enclosed each in a thick skin bag, resembling long- stemmed parasols with small shades. This struc- ture differs radically from that of the spines of all other ophiuran
. A contribution to American thalassography : Three cruises of the United States Coast and geodetic survey steamer "Blake", in the gulf of Mexico, in the Caribbean sea, and along the Atlantic coast of the United States, from 1877 to 1880. Blake (Steamer); Marine animals -- Atlantic Ocean; Marine sediments. 116 THREE CRUISES OF THE "; further examination showed these tufts to be bunches of minute spines enclosed each in a thick skin bag, resembling long- stemmed parasols with small shades. This struc- ture differs radically from that of the spines of all other ophiurans hitherto known where there is no Fig. 402. *. Fig. 403. -§°. Ophioheius umbeiia. (Lyman.) departure ±rom the single row of articulated spines. A bunch of these umbrella-shaped spines of Ophioheius um- is given in Fig. 403. The stalked crinoids are among the most interesting of the deep-sea animals. Their palaBontological relations run back in the case of the Pentacrinoidea and the Apiocrinidse (Rhizocrinus) to the Jurassic period ; while the relationship of Holopus may probably extend to the silurian (Edriocrinus). The , of which four species were known from the Caribbean district, are characterized by the verticillate ar- rangement of the cirri along the whole length of the stem, while in the Bourgueticrini the whole stem even may be free of cirri. Recent species of Pentacrinidse have been found both in the Pacific and Atlantic, and they are common at depths of less than 100 fathoms. The species of the genus Metacrinus (Fig. 404) replace in the Pacific, to a certain extent, the Atlantic Pen- tacrini. Our first accurate knowledge of the type dates from Miller, who compared the structure of the fossil species with that of both Pentacrinus asterius (Fig. 405) and the free Coma- tulse. This relationship was subsequently most satisfactorily proved by J. V. Thomson, who in 1836 discovered the penta- crinoid stage of a species of Comatula. (Fig. 40
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